Information about most Sacharomyces cerevisiae genes, whether newly discovered or previously identified, is very limited. We propose to utilize a new multipurpose transposon to construct a lacZ expression reporter for every gene in the yeast genome and an epitope-tagged version of every protein. Strains carrying lacZ reporters will he used to determine which genes are expressed during vegetative growth, sporulation and mating. Strains containing epitope-tagged proteins will be used to localize gene products by indirect immunofluorescence using antibodies directed against the epitope. Proteins that localize to the nucleus will be examined for localization to chromosomes through the analysis of spread preparations of meiotic nuclei. We will analyze strains containing insertion mutations in small ORFs, sporulation-induced genes and pheromone-regulated genes for defects in vegetative growth, sporulation and mating, respectively. Finally, a subset of epitope-tag insertions in essential genes will be analyzed for conditional growth defects. We expect this project to have significant impact on the scientific community. The information generated will be maintained in a data base accessible by Internet. Any researcher who identifies a yeast gene will be able to determine immediately whether that gene is expressed at a specific time during the life cycle and whether its gene product localizes to a specific subcellular location. Insertion libraries, plasmids, and yeast strains containing lacZ-reporter genes and epitope-tagged proteins will he made available to all interested researchers. These reagents are expected to be useful in many different types of studies. The technology proposed and the information gained will be applicable to the study of other organisms.